It is generally known in the art of manufacturing automotive glazings to heat a glass templet to a temperature above its plastic set temperature, usually about 1,200.degree. F., then form the templet to its desired curvature by either gravity forming or press bending the glass, and finally rapidly quench the formed glass sheet by directing streams of a tempering fluid, usually air, against the major surfaces thereof. During the tempering operation, it is known to support the formed glass sheet on a support ring, comprising a rigid structure conforming generally in outline and elevation to the peripheral marginal surface of the formed glass sheet. In some operations, the support ring is initially used for press bending the glass templet, or as a mold for gravity forming the glass templet to the desired final curvature, prior to its use as a tempering support ring.
During a glass tempering operation, blasts of tempering fluid rapidly cool the formed glass sheet in all areas, except the area of contact between the glass sheet and the support ring where cooling is retarded due to restricted tempering fluid flow. Thus, the majority of the cooled glass sheet is stressed in compression, while the area of the glass sheet which is adjacent the support ring is stressed in tension. This stress imbalance often leads to spontaneous breakage of the ultimately produced formed and tempered glass sheet. Moreover, uniform cooling of the surfaces of the formed glass sheet is practically impossible due to conductive heat transfer which occurs adjacent the areas of direct contact between the formed glass sheet and the support ring.
The support rings disclosed in the prior art generally were designed to allow increased tempering fluid flow and to minimize conductive heat transfer in the vicinity of the contact area between the formed glass sheet and support ring.
U.S. Pat. No. 3,089,319 to Carson et al. discloses a glass sheet gravity forming apparatus, including a support ring having solid metal rails which contact the peripheral marginal surface of the formed glass sheet. The device, having the formed glass sheet resting thereon, may be shuttled to a tempering station where blasts of tempering air are directed at the major surfaces of the glass sheet. The patent states that there is a compelling need for an absolute minimum of contact between the formed glass sheet and the support ring, to effect proper, uniform tempering.
U.S. Pat. No. 3,846,104 to Seymour discloses apparatus for handling glass sheets during shaping and cooling, including a conventional tempering ring with serations and apertures therein to reduce the glass sheet contact area and to increase the flow therearound of tempering air.
U.S. Pat. No. 3,973,943 to Seymour discloses a support ring for tempering a formed glass sheet, wherein a serated and apertured non-metallic ring is affixed to a conventional tempering ring. The peripheral marginal surface of the hot, formed glass sheet contacts only the non-metallic material during the tempering operation so as to minimize conductive heat transfer from the glass sheet to the support ring.
U.S. Pat. Nos. 2,408,526 to Minton and 3,310,273 to Seymour disclose formed glass sheet support rings having asbestos and wire mesh, respectively, placed over rigid support members, to reduce the amount of heat conducted from the glass sheets to the support rings.
U.S. Pat. Nos. 4,556,407 and 4,556,408 to Fecik et al. disclose formed glass sheet tempering rings having discrete upstanding support members including non-metallic support blocks which contact the peripheral marginal surfaces of the glass sheets.
Finally, U.S. Pat. No. 4,812,157 to Smith discloses a formed glass sheet support ring, comprising a support rail having a plurality of adjustable, upstanding stanchions with convex apecies. It is difficult, however, to initially establish a continuous series of glass sheet peripheral marginal surface contact points, since the elevation of each stanchion must be set individually in a fashion so that no single stanchion bears a substantially greater weight of the glass sheet than any adjacent stanchion (or the glass sheet will be deformed by the stanchion bearing the greater weight).
It would be desirable to create a glass sheet support ring configuration which could be assembled simply, and which would allow for greater tempering fluid flow therearound while minimizing the conductive heat transfer from the peripheral marginal surface of the formed glass sheet to the support ring. Such a ring could be used exclusively for supporting a formed glass sheet during a tempering operation, or could additionally be used as a press rail in a glass sheet press bending operation or as a mold ring in a glass sheet gravity forming operation.